PrincipalExtractor (Spring Boot API)

所有已知实现类:
FixedPrincipalExtractor
```
public interface PrincipalExtractor
```
Strategy used by UserInfoTokenServices to extract the principal from the resource server's response.
从以下版本开始:
1.4.0

- 方法概要
  所有方法实例方法抽象方法
  修饰符和类型方法说明
  Object extractPrincipal(Map<String,Object> map)
  Extract the principal that should be used for the token.

- 方法详细资料
  - extractPrincipal
```
Object extractPrincipal(Map<String,Object> map)
```
    Extract the principal that should be used for the token.
    参数:
    map - the source map
    返回:
    the extracted principal or null